1. Field of the Invention
The invention relates to optical communications devices, such as transmitters, receivers, and transceivers used in high throughput fiber optic communications links in local and wide area networks and storage networks, and in particular to parametric monitoring of the performance of such devices.
2. Description of the Related Art
Communications networks have experienced dramatic growth in data transmission traffic in recent years due to worldwide Internet access, e-mail, and e-commerce. As Internet usage grows to include transmission of larger data files, including content such as full motion video on-demand (including HDTV), multi-channel high quality audio, online video conferencing, image transfer, and other broadband applications, the delivery of such data will place a greater demand on available bandwidth. The bulk of this traffic is already routed through the optical networking infrastructure used by local and long distance carriers, as well as Internet service providers. Since optical fiber offers substantially greater bandwidth capacity, is less error prone, and is easier to administer than conventional copper wire technologies, it is not surprising to see increased deployment of optical fiber in data centers, storage area networks, and enterprise computer networks for short range network unit to network unit interconnection.
Such increased deployment has created a demand for electrical and optical transceiver modules that enable data system units such as computers, storage units, routers, and similar devices to be optionally coupled by either ran electrical cable or an optical fiber to provide a high speed, short reach (less than 50 meters) data link within the data center.
A variety of optical transceiver modules are known in the art to provide such interconnection that include an optical transmit portion that converts an electrical signal into a modulated light beam that is coupled to a first optical fiber, and a receive portion that receives a second optical signal from a second optical fiber and converts it into an electrical signal. The electrical signals are transferred in both directions over an electrical connectors that interface with the network unit using a standard electrical data link protocol.
The optical transmitter section includes one or more semiconductor lasers and an optical assembly to focus or direct the light from the lasers into an optical fiber, which in turn, is connected to a receptacle or connector on the transceiver to allow an external optical fiber to be connected thereto using a standard SC, FC or LC connector. The semiconductor lasers are typically packaged in a hermetically sealed can or similar housing in order to protect the laser from humidity or other harsh environmental conditions. The semiconductor laser chip is typically a distributed feedback (DFB) laser with dimensions a few hundred microns to a couple of millimeters wide and 100-500 microns thick. The package in which they are mounted typically includes a heat sink or spreader, and has several electrical leads coming out of the package to provide power and signal inputs to the laser chips. The electrical leads are then soldered to the circuit board in the optical transceiver. The optical receive section includes an optical assembly to focus or direct the light from the optical fiber onto a photodetector, which in turn, is connected to a transimpedance amplifier/limiter circuit on a circuit board. The photodetector or photodiode is typically packaged in a hermetically sealed package in order to protect it from harsh environmental conditions. The photodiodes are semiconductor chips that are typically a few hundred microns to a couple of millimeters wide and 100-500 microns thick. The package in which they are mounted is typically from three to six millimeters in diameter, and two to five millimeters tall and has several electrical leads coming out of the package. These electrical leads are then soldered to the circuit board containing the amplifier/limiter and other circuits for processing the electrical signal.
Optical transceiver modules are therefore packaged in a number of standard form factors which are “hot pluggable” into a rack mounted line card network unit or the chassis of the data system unit. Standard form factors set forth in Multiple Source Agreements provide standardized dimensions and input/output interfaces that allow devices from different manufacturers to be used interchangeably. Some of the most popular MSAs include XENPAK (see www.xenpak.org), X2 (see www.X2 msa.org), SFF (“small form factor”), SFP (“small form factor pluggable”), XFP (“10 Gigabit Small Form Factor Pluggable”, see www.XFPMSA.org), and the 300-pin module (see www.300pinmsa.org).
Customers and users of modules are interested in such miniaturized transceivers in order to increase the number of interconnections or port density associated with the network unit, such as, for example in rack mounted line cards, switch boxes, cabling patch panels, wiring closets, and computer I/O interfaces.
The reliability of such modules is an important consideration in the selection of specific designs for many commercial applications. When a module fails, users typically wish to know why. This interest is not a matter of idle curiosity; it is based on a generally accepted belief that knowing the root cause of a failure is an essential step in preventing recurrence of that failure. Thus, producers of optical modules expend much effort in failure analysis to determine the root cause of any failures that occur and to subsequently improve products to eliminate similar failures in the future. Such failure analysis is often very labor intensive, requiring technologists referred to as reliability analysts. Such failure analysis often requires an extensive suite of test equipment, which also represents a significant expense to the manufacturer.
The failure analysis process is relatively expensive to the manufacturer, and consequently one has an interest in conducting the analysis as efficiently as possible. Additionally, sometimes the failure is covered by a warranty, and honoring the warranty represents an expense to the manufacturer.
Conversely, sometimes the failure is a result of unduly harsh use by the user outside of normal environmental conditions, or some other circumstance that voids the warranty (such as use with incompatible equipment), and proving that the terms of the warranty have been violated can enable the manufacturer to avoid expense, particularly when the user chooses to return large quantities of product for purported warranty service.
If more information regarding the actual operational history of the optical module could be made available during the failure analysis, then determining the validity of the warranty status would be made more straightforward, and aspects of the failure analysis would be simpler. Failure analysis involves a search for information about the causes and circumstances of product failure, often by exploiting very subtle clues, and any information that can be made explicitly available to the reliability analyst has the potential to make their task more productive, effective, and efficient.
This process of failure analysis is extendable to cases in which no failure has occurred. In this case, a reliability analyst may analyze a used optical module to observe parametric shifts in performance, and the information gained may be used to define design and manufacturing process improvements to make the product even more reliable in the future. Because of the importance of reducing failures and parametric shifts in product performance, a need exists for better methods of tracking the environmental and operational conditions under which an optoelectronic module or product is used in the field, i.e. in actual customer installation.